A breathing apparatus, in which the oxygen needed for breathing is generated by the thermal decomposition of a chemical, has become known from German Patent No. DE-PS 679 503. The oxygen-generating chemical is accommodated in the interior of a cylindrical cartridge housing and is activated by means of an igniting composition located at one of the ends of the cartridge. A feed line with a restrictor, via which line the oxygen generated is fed into a breathing bag, from which the user of the breathing apparatus receives his breathing gas, is connected to the opposite end of the cartridge. The reaction temperature of approx. 300.degree. C. to 800.degree. C. necessary for the chemical reaction is generated by the igniting composition in the chemical in contact with the igniting composition. A reaction front develops in the area of the igniting composition and gradually propagates in the interior of the cartridge housing in the direction of the yet unreacted chemical, develops in the area of the igniting composition. Dusts and gases, which act on the yet unreacted chemical particles as a reaction-accelerating catalyst, are formed during the reaction within the reaction front. The amount of oxygen generated per unit of time also increases in a chemical reaction that takes place in an accelerated manner.
The disadvantage of the prior-art breathing apparatus is that the flow of oxygen supplied from the cartridge is generally subject to great variations, because the thermal decomposition depends on the design of the cartridge and the ambient temperature, and it takes place, in general, nonuniformly. Even though the course of the chemical reaction over time can be improved by a special cartridge design, e.g., with reaction control elements or with heat-conducting plates within the chemical, these measures markedly increase the manufacturing costs, especially because the cartridge is a disposable item.